It is effective conventionally to use electret as a device that generates electric power by vibrating in the environment (energy harvesters), and many research and development have been performed in this field. As vibration-powered electricity generating devices, primarily used as power sources for various types of wireless standalone sensors and as power sources for wireless communication devices engaged in exchange of signals by such wireless standalone sensors, they need to be compact and capable of generating significant amounts of power (in a μW through mW range). A vibration energy harvester disclosed in PTL1, for instance, generates power by inducing a vibrating electrode to vibrate relative to an electrode with an electret formed thereat.